As an easy method to measure the glucose level in blood, a disposable glucose sensor is often utilized (See Patent Document 1, for example). For instance, the glucose sensor may be designed to output the response current, which is necessary for computing the blood glucose level, when it is mounted to an analytical apparatus. In the analytical apparatus, the magnitude of the response current is determined by utilizing a double integration circuit including a capacitor, and the blood glucose level is computed based on the determined response current. As shown in FIGS. 11A and 11B, the magnitude of the response current is determined based on the discharge time (T2) of the capacitor after the capacitor is charged with the electric charge related with the response current for a predetermined time period (T1). As shown in FIG. 12, the determination of the response current is performed at predetermined time intervals (t). On the other hand, the response current (I1) for computing the blood glucose level is sampled at the time (t1) after a predetermined time period has elapsed from the time (t0) when the supply of the blood to the glucose sensor was confirmed. The blood supply to the glucose sensor is confirmed by checking whether or not the response current measured exceeds a predetermined threshold (I2).
To accurately determine the response value by the method utilizing the double integration circuit, it is preferable to set the charge time (T1) of the capacitor relatively long. Therefore, for the measurement accuracy of the response current, the time interval (t) for measuring the response current need be set relatively long.
As will be understood from FIG. 12, in the initial stage in which the blood is supplied to the glucose sensor, the response current increases sharply. Therefore, in the case where the time interval (t) for measuring the response current is set long, the time when the blood is supplied cannot be determined accurately. Due to such inaccuracy, the time period from when the sample is supplied till when the response current for the computation is sampled may vary among the measurements, which may degrade the measurement accuracy of the blood glucose level.
Patent Document 1: JP-B-H08-10208